Friday, December 30, 2016

Docker Compose is a tool for defining and running multi-container applications. In this post I will show you how you can create two containers. One will host a PostgreSQL database and the other will host an ASP.NET Core website. Docker Compose will build a virtual network that allows both containers to communicate with each other.

PostgreSQL is an open source relational database management system ( DBMS ) developed by a worldwide team of volunteers. PostgreSQL is not controlled by any corporation or other private entity and the source code is available free of charge.

4) Startup.cs file – automatic database migration

Also, in the Startup.cs file find the Configure() method. We will use dependency injection to get an instance of the database ApplicationDbContext context class. To do this, add an additional argument to the Configure() method so that its signature looks like this:

We will be using the official Microsoft docker container named microsoft/aspnetcore-build:1.0.3-projectjson as our starting image. This is a suitable container because it already has the .NET Core sdk + npm + bower. Also, it is based on .NET Core version 1.0, which is compatible to our web app.

ENTRYPOINT ["dotnet", "run"]

The web application will be started by executing the “dotnet run” command which starts the web server.

ENV ASPNETCORE_ENVIRONMENT=Development

We are setting the ASPNETCORE_ENVIRONMENT environment variable so that we can see detailed error messages. In production, you will change this to Production.

WORKDIR /app

A directory named /app is created in the Linux container to host our source code.

COPY . .

Our source code is copied from the YoAspnet folder on our Windows 10 computer to the /app folder in the Linux container.

RUN dotnet restore

This command executes “dotnet restore” in the /app folder in the Linux container.

RUN build

This command will build the application

EXPOSE 80

Port 80 is the port number that will be exposed by the container.

docker-compose.yml

Create a text file in the AspnetPostgres folder named docker-compose.yml and add to it the following content:

Container db will host the PostgresSQL database server. This container is built using the postgres image, which will be downloaded from http://hub.docker.com. A user named docker will be created also with password docker.

Container app will host our ASP.NET Core 1.0 application. This container is dependent on container db. The internal container port 80 will be exposed to the host as port 88. The context of the build process will be the current directory and the build process is defined in the Dockerfile.linux file, which we already scripted.

Executing docker-compose.yml

In a command-prompt, execute the following command in order to run docker-compose.yml:

docker-compose up

The instructions in the docker-compose.yml file will take about two minutes to complete. When it is done, you will see that the Kestrel web server is listening on port 80:

Open another instance of a terminal window and execute the following command to find out how many containers are running:

docker ps

There are two containers running. One is named aspnetpostgres_app_1 and the other is named aspnetpostgres_db_1.

Find out what virtual networks were created by executing the following command:

docker network ls

This reveals that a network named aspnetpostgres_default was created which both containers use to communicate with one-another:

Let us also find out where the data is being saved. Type the following command:

docker volume ls

This shows that a volume was created by PostGresSQL for the data:

This database volume will not be deleted automatically when the container is stopped or removed.

Now for the moment you have been waiting for: Point your browser to http://localhost:88. You should see our website being served from the ASP.NET Core 1.0 container:

Click on Register in the top-right corner and enter a user email and password:

After clicking on the Register button, you should see that the new user was indeed created:

Cleanup

Stop the terminal window that you used for docker-compose by hitting CTRL + C on the keyboard.
Type the following command to tear down all the containers and networks that were created by docker-compose.yml:

docker-compose down

At this stage, the database volume will still exist. To delete the database volume, type the following command: